Fix address family config generated for MX

- Address family names are slightly different in junos from what we have in
contrail. We now maintain a map to convert from contrail to junos.
- We were not programming families on session if there were any configured.
Added support for that.
- Added test case for the same

Change-Id: I43412427a013dd73087dbd6174172ef424664161
Merge "Fix address family config generated for MX"